AUSTIN, TX - MARCH 09: Director Richard Linklater arrives at the premiere of "Boyhood" at the 2014 SXSW Music, Film + Interactive Festival at the Paramount Theatre on March 9, 2014 in Austin, Texas. (Photo by Michael Buckner/Getty Images for SXSW)

Ever since his gonzo debut documentary “Slacker” (1991), Texas filmmaker Richard Linklater has interspersed formal experiments (the “Before” trilogy with Ethan Hawke and Julie Delpy, the digitally rotoscoped “Waking Life” and “A Scanner Darkly”) with more conventional movies such as “Dazed and Confused” and “School of Rock.”

But nothing he’s done has been quite as ambitious as “Boyhood” (July 12). Over the course of 12 years, for a few days each summer, Linklater shot a young Austin lad, Ellar Coltrane, playing a boy named Mason. The resulting film, in which Hawke and Patricia Arquette play Mason’s parents, charts his actual as well as fictional growth from age 6 to 18.

“This is the biggest one yet, certainly as far as time commitment and on the level of something that you haven’t seen before,” reckons Linklater, 53. “It’s a unique process, in one film, to watch everybody age 12 years.”

The director admits that autobiographical elements figure in his coming-of-age scenario, especially when it came to casting Mason’s sibling Samantha.

“Lorelei, my daughter, plays the older sister, a part she demanded back then,” Linklater reveals. “She’d been in my film ‘Waking Life,’ had just kind of grown up on movie stuff. There was a logistical uncertainty, obviously, about knowing where the kids are every year and keeping up with them. So it made sense that I could at least keep tabs on her. And she wanted to do it at the time; about three years in, she was asking if a kid or two could be killed off or something.”

How much of Ellar, though, will we see in Mason?

“I wasn’t really following Ellar; just keeping up with him,” Linklater says. “The film is a narrative, it was all scripted and rehearsed. But that was certainly the big question. You look at a 6-year-old and go, what kind of teenager and young adult are you going to be? You never knew. I took a hunch, and he’s this really thoughtful, mysterious and interesting young man now. But that’s kind of who he was at 6.”